My 86 W124 has no air due to broken compressor and in Seattle (chronic rain at 40-55 F) I have absolutely no problem defrosting. In fact I rarely use defrost in either car.

Keep glass clean -- I use Stoner Invisible Glass (no amonia).

I suspect your recircualtion flap is stuck closed somehow (your air is always recirc even if button is not depressed) it is nearly impossible to defrost on recirc.

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David
1986 300E Anthracite + ECodes + MB Mileage Award